We investigate the nature and possible formation processes of three areas on Titan's surface which have been suggested as geologically interesting: Hotei Regio, Tui Regio, and Sotra Patera. We also reanalyze the spectral characteristics of the Huygens Landing Site. We apply a statistical Principal Component Analysis (PCA) and a radiative transfer (RT) method on the Visual and Infrared Mapping Spectrometer Datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared. We have been able to exploit only a subset of the currently available Hotei Regio data, which are, in general, not optimal in terms of geometry for an analysis with a plane-parallel RT code. Our inferred surface albedos present generally higher values from 1 to 2 μm and lower ones at 0.94 and in the 2.6-5 μm region. The Regions of Interest (RoIs) within Hotei Regio, Tui Regio, and Sotra Patera are always significantly brighter than the surrounding areas. The largest variations are found longward of 2 μm and mainly at 5 μm. This higher surface albedo with respect to the surrounding area and, in general, the fact that the spectral behavior is different for each of these areas, is probably indicative of diverse chemical compositions and origins. We compare the spectral albedos with some suggested surface candidates on Titan (such as H 2 O, CO 2 , and CH 4 ices, as well as tholin) and discuss possible chemical composition variations as well as other interpretations.

Greece, a country characterised by intense seismic and volcanic activity, has a complex geodynamic and geological setting that favours the occurrence of many gas manifestations. In this study, we address the origin of CH 4 and light hydrocarbons in cold and thermal emissions discharging along the Hellenic territory. Also, we investigate their possible relationship with the main geochemical composition of the gases and the different geological settings of the sampling sites. For this purpose we collected 101 new samples that were analysed for their chemical (O 2 , N 2 , CH 4 , CO 2 , He, Ne, Ar, H 2 , H 2 S and C 2 -C 6 hydrocarbons) and isotopic (R/R A , δ 13 C-CO 2 , δ 13 C-CH 4 and δ 2 H-CH 4 ) composition. Results show that CH 4 presents a wide range of concentrations (from < 0.5 to 925,200 μmol/mol) and isotopic values (δ 13 C-CH 4 from −79.8 to +45.0‰ vs. V-PDB; δ 2 H-CH 4 from −311 to +301‰ vs. V-SMOW). Greece was subdivided in four geologic units (External [EH] and Internal [IH] Hellenides, Hellenic Hinterland [HH] and active Volcanic Arc [VA]) and a decreasing CH 4 concentration from EH to HH was recognized, whereas CH 4 showed intermediate concentrations in VA. The CH 4 /(C 2 H 6 + C 3 H 8 ) ratios (from 1.5 to 93,200), coupled with CH 4 isotopic features, suggest that the light alkanes derive from different primary sources and are affected by secondary processes. An almost exclusive biotic, mainly microbial, origin of CH 4 can be attributed to EH gases. Cold gases at IH have mainly a thermogenic origin, although some gases connected to continental serpentinization may have an abiogenic origin. Methane in gases bubbling in thermal waters of IH, HH and VA and fumarolic gases of the VA seem to have an abiogenic origin, although their chemical and isotopic characteristics may have been produced by secondary oxidation of thermogenic CH 4 , a process that in some of the sampled gases causes extremely positive isotopic values (δ 13 C-CH 4 up to +45.0‰ vs. V-PDB and δ 2 H-CH 4 up to +301‰ vs. V-SMOW).

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